Conventionally, a radiant tube burner has been manufactured in which a completely premixed gas of a fuel gas and combustion air is combusted in a heat-resistant round tube (radiator tube) to thereby use the resulting flame to cause the radiator tube to be red hot. Such the radiant tube burner is used as an elongated heat source without exposure of a flame in heating furnaces and heaters. Furthermore a combustion burner is known in which combustion gas is combusted in an inner tube and a direction of flow is varied by collision of a jet of combustion gas with a shield surface disposed orthogonally thereto to thereby extract heat from the radiator tube.
In this type of combustion heater, since combustion is terminated midway in the radiator tube, disadvantages include the fact that there are difficulties to obtain a uniform temperature distribution along the entire tube length, and the fact that a large amount of nitrogen oxides (NOx) is produced. In Patent Literature 1, a combustion heater is disclosed which includes a porous tube having an inner section acting as a supply passage for a premixed gas, and a radiator tube disposed coaxially to the outer periphery of the porous tube. A premixed gas is ejected radially from the porous tube and forms laminar flow. Combustion of the premixed gas is executed on a cylindrical surface between the radiator tube and the porous tube on which the rate of flow of the premixed gas balances the flame propagation speed to thereby obtain a higher uniform temperature on the whole of the radiator tube and facilitate high heat generation and low NOx production.
[Patent Literature 1] Japanese Patent Application, First Publication No. 6-241419